The proposed research is designed to understand more fully the shape and size determining mechanisms in viral morphogenesis using bacterial viruses as an experimental system. The experiments proposed here will help provide molecular explanations for the mechanisms of head length and tail length regulation as well as DNA organization within the viral capsid. We plan to examine the geometry of T4 heads and estabilsh the extent and variation in head length by electron microscopic methods. Immuno-electron microscopy will be used to locate proteins in the headtail connector, and we shall examine isometric SPO1 and T4 heads by X-ray diffraction to determine their long-range DNA order. Experiments are planned to examine the role of genes 20 and 40 in T4 head morphogenesis and to test models of head length regulation by "gene dosage" mixed infections using wild type and amber mutant phage. Tail length regulation will be studied by analyzing the proteins attached to the tail tube after limited dissociation of baseplates by various agents and by gene dosage experiments. Tail tube structure will be explored using oriented sols of partially dissociated tail tube-baseplates and low angle X-ray diffraction.